Methods and Apparatus of Guard Rings for Wafer-Level-Packaging

ABSTRACT

Methods and apparatuses are disclosed for forming a post-passivation interconnect (PPI) guard ring over a circuit in a wafer forming a wafer level package (WLP). A circuit device comprises a guard ring and an active area. A passivation layer is formed on top of the circuit device over the guard ring and the active area, wherein the passivation layer contains a passivation contact connected to the guard ring. A first polymer layer is formed over the passivation layer. A PPI opening is formed within the first polymer layer or within the passivation layer over the passivation contact. A PPI guard ring is formed filling the PPI opening in touch with the passivation contact and extending on top of the first polymer layer or the passivation layer.

BACKGROUND

Since the invention of the integrated circuit (IC), the semiconductorindustry has experienced rapid growth due to continuous improvements inthe integration density of a variety of electronic components. For themost part, this improvement in integration density has come fromrepeated reductions in minimum feature size, which allows morecomponents to be integrated into a given area. As the demand for evensmaller electronic devices has grown, there has grown a need for smallerand more creative packaging techniques of semiconductor dies.

Conventional package technologies divide a wafer into separate dies andpackage each individual die; therefore, these techniques are timeconsuming. The trend of package technique is toward ball grid array(BGA), flip chip (FC-BGA), chip scale package (CSP), and wafer levelpackage (WLP). Wafer level packaging technology can produce dies withextremely small dimensions and good electrical properties, and iscurrently widely used for its low cost and relatively simple processes.

During the manufacture and operation of the integrated circuit, the dieis subjected to mechanical stress, cracks, and moisture penetrations.The stress may be especially high near the edges and the corners of thedie. As the die is stressed, active devices, passive devices, andinterconnects that make up the integrated circuit are also stressed,which may cause a mechanical failure of the devices or interconnects. Inorder to prevent such stresses and failures, a guard ring is usuallymanufactured around the edge of individual circuits. The guard ring onthe circuit prevents stresses of the dielectric and metal layers of thecircuit. However, guard ring on the circuit level may not be enough toprevent all the possible stresses and damages to the circuits in apackage, particularly with WLP technology.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1( a)-1(c) illustrate a part of a wafer with scribe lines, dieswith bonding pads, active areas, and circuit guard rings, covered bypassivation layers; and

FIGS. 2( a)-2(c) illustrate various embodiments of post-passivationinterconnect (PPI) guard rings on top of the passivation layers.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the present disclosure arediscussed in detail below. It should be appreciated, however, that theembodiments of the present disclosure provide many applicable conceptsthat can be embodied in a wide variety of specific contexts. Thespecific embodiments discussed are merely illustrative of specific waysto make and use the disclosure, and do not limit the scope of thedisclosure.

As will be illustrated below for a WLP process, interconnect structuresare formed on metallization layers of a circuit device. Passivationlayers are formed over the top metallization layer. Polymer layers maybe formed on top of the passivation layers. Post-passivationinterconnect (PPI) pads and PPI guard rings are then formed on top ofthe polymer layer or the passivation layers. The PPI guard rings maystop the moisture and crack penetrating into the circuit device.

FIG. 1( a) illustrates a surface view of the top side of an integratedcircuit (IC) device 11. The circuit device 11 may be made up of millionsof components such as active devices and passive devices. Thesecomponents are initially isolated from each other, formed on anunderlying silicon substrate, and are later interconnected together bymetal interconnect lines to form the functional circuit. Typicalinterconnect structures include lateral interconnections, such as metallines or wirings, and vertical interconnections, such as vias andcontacts. The side of the silicon substrate on which the integratedcircuit is formed may be referred to as the top side of the circuitdevice. An integrated circuit device may be referred as a circuit, adevice, a circuit device, an integrated circuit device, a die, or in anyother terms known to those skilled in the art.

As illustrated in FIG. 1( a), bond pads 32 are located along theperiphery of the integrated circuit device 11. In the center of theintegrated circuit device 11 is the active region 12 containing themajority of the high density, active circuitry of the integrated circuitdevice 11. Voltage signals may be supplied to the circuitry within theactive region 12 by way of the bond pads 32. These voltage signals aresupplied to the bond pads 32 through a package to which the integratedcircuit device 11 is affixed.

The integrated circuit device 11 is surrounded by a guard ring region 34where a guard ring may be formed, not shown. The guard ring region 34may be generally referred as the guard ring 34. Guard ring is generallyformed of conductive materials similar to bond pads 32, such as forexample aluminum (Al), aluminum-copper (Al—Cu) alloy, oraluminum-copper-silicon (Al—Cu—Si) alloy. The guard ring 34 is placedoutside of bond pads 32 and protects the integrated circuit device 11.The guard ring 34 is a circuit guard ring located on the circuit, andmay be referred as a seal ring as well. The guard ring 34 has two edges,outer edge 131 is also a chip edge, while another edge 133 is adjacentto the bond pads and the active area, separating the guard ring 34 fromthe bond pads and the active area. For some embodiments, the size of theguard ring from one edge 131 to another edge 133 may be of a size about10 um.

FIG. 1( b) is an expanded view of a portion of a wafer 25 showingindividual integrated circuit devices 30 and 35 separated by a scribeline 37. Wafers are used as carriers for fabrication during theproduction of integrated circuit devices. After semiconductorfabrication processes, a plurality of dies such as 30 and 35 is formedon a wafer. These dies are later separated through a die cutting orsingulation process in which typically a mechanical or laser saw is usedto cut through the wafer between individual chips or dies. To facilitatethe die cutting process, relatively narrow sacrificial scribe lines 37are provided on the wafer along which the cuts are made to separate thedies. As shown in FIG. 1( b), the scribe line 37 is surrounded by twoedges 131 and 132, where the edge 131 is a chip edge for the device 30and the edge 132 is a chip edge for the device 35. The scribe line 37may include a plurality of test pads 39 for testing the integratedcircuits 30 and 35.

The integrated circuit device 30 has bond pads 32 located around theperiphery of the top surface of the device, and is surrounded by a guardring 34, where the guard ring 34 has edges 131 and 133. The edge 131 isthe chip edge next to the scribe line and the edge 133 is the guard ringedge adjacent to the bond pad and the active area. Similarly, theintegrated circuit device 35 has bond pads 33 located around theperiphery of the top surface of the device, and is surrounded by a guardring 36, where the guard ring 36 has edges 132 and 134. The edge 132 isthe chip edge next to the scribe line and the edge 134 is the guard ringedge adjacent to the bond pad and the active area.

FIG. 1( b) shows the top conductive (e.g., metal) line of the integratedcircuit devices 30 and 35. In general, after the devices are fabricated,bond pads 32 and 33 and test pad 39 lie beneath dielectric layers andmust be exposed for testing and bonding to a suitable package.

As illustrated in FIG. 1( c), the bond pads 32 and 33, the guard rings34 and 36, and the test pads 39 may be covered by a passivation layer. Apassivation layer may be formed of a non-organic material selected fromun-doped silicate glass (USG), silicon nitride, silicon oxynitride,silicon oxide, and combinations thereof. The passivation layerillustrated in FIG. 1( c) may comprise a plurality of sub-layers. Afirst passivation layer 40 may be deposited conformal to the top metalstructure of the circuits 30 and 35. The first passivation layer 40 maybe made of silicon nitride. On top of the first passivation layer 40, asecond passivation layer 45 may be deposited conformal to the top of thefirst passivation layer 40. In an embodiment, the first passivationlayer 40 is formed of a relative-hard material, and the secondpassivation layer 45 is formed of a relative-soft material. Together,the hard and soft passivation layers protect the device from theambient, for example, scratches, moisture, and impurities. The number ofpassivation layers shown in FIG. 1( c) is only for illustration purposesand is not limiting. There may be only one passivation layer, or aplurality of passivation sub-layers formed on top of the circuitdevices. A passivation layer may be used to refer to a sub-layer or theoverall passivation layer.

According to some embodiments of the WLP process disclosed, after apassivation layer or a plurality of passivation sub-layers are formedover the top metallization layer, as shown in FIGS. 1( a)-1(c), polymerlayers may be formed on top of the passivation layers. Post-passivationinterconnect (PPI) pads and PPI guard rings are then formed on top ofthe polymer layer or the passivation layer, which will be illustrated inFIGS. 2( a)-2(c). In order to complete the WLP process, under-bumpmetallurgy (UBM) layers will be formed, which is not shown. FIGS. 2(a)-2(c) illustrate only structures formed over one circuit device 30 ofFIG. 1( c). Similar structures may be formed over other circuit device35 in the wafer shown in FIG. 1( c).

Illustrated in FIG. 2( a), vias 401 and 405 are formed in the firstpassivation layer. In an embodiment, the via 401 is on top of the bondpad 32, and the via 405 is on top of the guard ring 34. In anembodiment, the via 401 is smaller than the size of the bond pad 32. Forexample, vias 401 and 405 have a size of equal to or greater than about2 μm×2 μm. In an exemplary embodiment, the vias 401 and 405 have a sizeof about 3 μm×3 μm. The vias 401 and 405 may be of different sizes.

Illustrated in FIG. 2( a), pads 402 and 406 are formed in the secondpassivation layer 45. In an embodiment, the pad 402 is over the via 401,and the pad 406 is over the via 405. The height and width of the pads402 and 406 may vary. The size of the pad 406 may be in a range of about3 um to 5 um. There may be a plurality of pads 402 and some of the pad402 may be over the active area of the circuit device.

The pad 406 and the via 405 together may be referred as a passivationcontact formed within the passivation layer. Similarly the pad 402 andthe via 401 may be another passivation contact formed within thepassivation layer. The passivation contact of pad 406 and via 405 may beat a same height as the passivation layer surface, or it can be lowerthan the passivation layer surface, as shown of the pad 402 and the via401. There may be different number of passivation layers such as onelayer or more than two sub-layers. A passivation contact may be formedin various steps through the passivation sub-layers to connect the guardring 34 or the bond pad 32 covered by the passivation layer to othercontacts on top of the passivation layer. A passivation contact may beformed in one step through multiple passivation sub-layers, or inmultiple steps.

A first polymer layer 51 may then be formed on top of the passivationlayer 45. In an embodiment, the first polymer layer 51 is formed overthe guard ring and the active areas, and not on the scribe line area asshown in FIG. 2( a). The first polymer layer 51 may be formed of apolymer, such as an epoxy, polyimide, benzocyclobutene (BCB),polybenzoxazole (PBO), and the like, although other relatively soft,often organic, dielectric materials can also be used. The formationmethods include spin coating or other commonly used methods. Thethickness of the first polymer layer 51 may be preferably between about5 μm and about 30 μm. The dimensions recited throughout the descriptionare merely examples, and will change with the down-scaling of integratedcircuits. The first polymer layer 51 may stop at a point before reachingthe chip edge 131, leaving a gap 201 between one end of the firstpolymer layer 51 and the chip edge 131. The size of the gap 201 may beabout 2 um for example. The first polymer layer may reach all the way tothe chip edge 131, so that the size of the gap 201 is 0.

The first polymer layer 51 may be patterned to form an opening to exposethe pad 406 over the guard ring 34. The opening may be referred as apost-passivation interconnect (PPI) opening since it may be used to forma PPI structure such as a PPI guard ring or a PPI via later. Thepatterning of the first polymer layer 51 may include photolithographytechniques. Next, the PPI opening may be filled with the metallicmaterial to form a via 407. The size of the via 407 may be in the rangeof about 2 um for the diameter of the via 407. The same metallicmaterial may further form a PPI pad 408 on top of the first polymerlayer 51. The formation methods include plating, electroless plating,sputtering, chemical vapor deposition methods, and the like. The fillingmaterial for the via 407 and the PPI pad 408 includes copper or copperalloys. Other metals, such as aluminum, silver, gold, and combinationsthereof, may also be included.

The PPI pad 408 and the via 407 together may be referred to as apost-passivation interconnect (PPI) guard ring over the guard ring 34.The PPI guard ring is on top of the passivation contact comprising pad406 and via 405. The PPI pad 408 is the part of the PPI guard ring ontop of the first polymer layer 51. The edge of the PPI pad 408 may havea distance 202 to the edge of the first polymer layer 51 on one side,and another distance 203 to the guard ring edge 133 on the other side.The two distances 202 and 203 may be of the same or similar sizes, inthe range of 2 um for example. The PPI pad 408 may be of a rectangleshape or a square shape, with one side of size around 4 um. For example,the PPI pad 408 may have a thickness of less than about 30 μm, or athickness between about 2 μm and about 10 μm.

Similarly, the first polymer layer 51 may be patterned to form anotherPPI opening to expose the pad 402 within the passivation layer over thebond pad 32. The opening shown in FIG. 2( a) may extend into thepassivation layer since the surface of the pad 402 is lower than thesurface of the passivation layer 45. Next, the opening may be filledwith the metallic material to form a via 403, which is partially intothe passivation layer 45. The same metallic material may further form apad 404 on top of the first polymer layer 51. The size of the vias 403and 407 may be of similar sizes of vias 401 and 405. They may be ofdifferent sizes as well. The pad 404 may be referred to aspost-passivation interconnect (PPI) pad. The PPI pad 404 may be used toconnect the bonding pad 32 to solder balls in the package.

A second polymer layer 52 is then formed and patterned on top of thefirst polymer layer 51, on top of the PPI pads 404 and 408. The secondpolymer layer 52 extends to the chip edge, and not over the scribe line.The second polymer layer 52 may also include a polymer selected from anepoxy, polyimide, BCB, and PBO, and may be patterned using the samemethod as patterning the first polymer layer 51.

Other additional layers such as UBM seed layer may be blanket formed,which may include a titanium layer and a copper seed layer on titaniumlayer. Alternatively UBM seed layer may include layers selected from achromium copper layer on a chromium layer, a copper layer on a titaniumtungsten layer, a nickel vanadium layer on an aluminum layer, a nickelvanadium layer on a titanium layer, or other combinations of theabove-mentioned layers. The UBM layer is over the second polymer layerand may be electrically connected to the PPI pad 404 which is furtherconnected to the bond pad 32 of the circuit.

FIG. 2( b) illustrates another embodiment of a PPI guard ring formed ontop of the guard ring 34. A passivation contact comprising a pad 406 anda via 405 may be formed within the passivation layers 40 and 45. A firstpolymer layer 51 may be formed on top of the passivation layer 45.Different from the embodiment shown in FIG. 2( a), the first polymerlayer 51 comprising two parts discontinuous from each other. A firstpart of the first polymer layer 51 is over the guard ring, which isdiscontinuous from a second part of the first polymer layer 51 whichends at an edge of the guard ring and over the active area. There is agap 204 between the two parts of the first polymer layer 51. The size ofthe gap may be about a size of 2 um. The discontinuous two parts of thefirst polymer layer 51 can further stop the crack ad moisturepenetration into the active area of the circuit.

Illustrated in FIG. 2( b), the first polymer layer 51 may be patternedto form a PPI opening to expose the pad 406 and via 405 on top of theguard ring 34. The PPI opening may go through the first polymer layer 51and extends into the passivation layer 45. Therefore the PPI opening maybe filled with the metallic material to form a via 407 which ispartially within the passivation layer. The same metallic material mayfurther form a PPI pad 408 on top of the first polymer layer 51. The PPIpad 408 and the via 407 may be referred to as post-passivationinterconnect (PPI) guard ring over the circuit guard ring 34, which areon top of the passivation contact of pad 406 and via 405. The PPI pad408 is the part of the PPI guard ring on top of the first polymer layer51. Other parts of FIG. 2( b) are similar to the descriptions of FIG. 2(a).

FIG. 2( c) illustrates another embodiment of a PPI guard ring formed ontop of the circuit guard ring 34. A passivation contact comprising a pad406 and a via 405 may be formed within the passivation layers 40 and 45.A first polymer layer 51 may be formed on top of the passivation layer45. Different from the embodiments shown in FIGS. 2( a) and 2(b), thefirst polymer layer 51 stops at the guard ring edge and does not extendto the guard ring area. A PPI opening may be formed directly in thepassivation layer 45 to expose the pad 406 and via 405 on top of theguard ring 34. Then the PPI opening may be filled with the metallicmaterial to form a via 407 which is within the passivation layer 45. Thesame metallic material may further form a PPI pad 408 on top of thepassivation layer 45. The PPI pad 408 and the via 407 may be referred toas a post-passivation interconnect (PPI) guard ring. The PPI guard ringmay be made of copper, copper alloys. aluminum, silver, gold, orcombinations thereof. The PPI guard ring is on top of the passivationcontact of pad 406 and via 405 over the circuit guard ring 34. The PPIpad 408 is the part of the PPI guard ring on top of the passivationlayer 45. An edge of the PPI guard ring over the passivation layer,which is an edge of the PPI pad 408, has a distance about 2 um or biggerto an edge of the first polymer layer, shown as the distance 203.Similar distance may be formed for another edge of the PPI pad 408 tothe chip edge, shown as the distance 202.

The first polymer layer 51 over the active area may be patterned to forma PPI opening to expose the pad 402 and via 401 within the passivationlayer on top of the bond pad 32. The opening shown in FIG. 2( c) mayextend into the passivation layer since the surface of the pad 402 islower than the surface of the passivation layer 45. Next, the openingmay be filled with the metallic material to form a via 403, which ispartially into the passivation layer 45. The same metallic material mayfurther form a pad 404 on top of the first polymer layer 51. The size ofthe vias 403 and 407 may be of similar sizes of vias 401 and 405. Theymay be of different sizes as well. The pad 404 may be referred to aspost-passivation interconnect (PPI) pad. The PPI pad 404 may be used toconnect the bonding pad 32 to solder balls in the package. Other partsof FIG. 2( c) are similar to the descriptions of FIG. 2( a).

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A semiconductor device, comprising: a circuitdevice comprising a guard ring and an active area; a passivation layeron the circuit device over the guard ring and the active area, whereinthe passivation layer comprises a passivation contact connected to theguard ring; a first polymer layer over the passivation layer, whereinthe first polymer layer has a post-passivation interconnect (PPI)opening over the guard ring; a PPI guard ring filling the PPI openingconnected to the passivation contact and extending on top of the firstpolymer layer; and a second polymer layer over the first polymer layerand the PPI guard ring.
 2. The semiconductor device of claim 1, whereinthe passivation layer comprises a plurality of sub-layers.
 3. Thesemiconductor device of claim 1, wherein the first polymer layer extendsto an edge of the guard ring next to a scribe line.
 4. The semiconductordevice of claim 1, wherein the PPI opening is of a round shape with adiameter about 2 um and the PPI guard ring on top of the first polymerlayer is of a square shape with a side of size about 4 um.
 5. Thesemiconductor device of claim 1, wherein an edge of the PPI guard ringon top of the first polymer layer has a distance about at least 2 um toan edge of the first polymer layer.
 6. The semiconductor device of claim1, wherein an edge of the PPI guard ring on top of the first polymerlayer has a distance about at least 2 um to an edge of the guard ringnext to the active area.
 7. The semiconductor device of claim 1, whereinthe PPI guard ring is made of copper, copper alloy, aluminum, silver,gold, or combinations thereof.
 8. The semiconductor device of claim 1,wherein the first polymer layer is made of an epoxy, polyimide,benzocyclobutene (BCB), polybenzoxazole (PBO), or other polymermaterial.
 9. The semiconductor device of claim 1, further comprising aPPI pad on top of the first polymer layer connected to a bonding pad ofthe circuit device.
 10. The semiconductor device of claim 9, furthercomprising an under-bump metallurgy (UBM) layer over the second polymerlayer electrically connected to the PPI pad.
 11. The semiconductordevice of claim 1, wherein the first polymer layer comprising a firstpart over the guard ring discontinuous from a second part ending at anedge of the guard ring and over the active area.
 12. The semiconductordevice of claim 11, wherein a gap between the first part of the firstpolymer layer and the second part of the first polymer layer is about asize of 2 um.
 13. A semiconductor device, comprising: a circuit devicecomprising a guard ring and an active area; a passivation layer on topof the circuit device over the guard ring and the active area, whereinthe passivation layer has a passivation contact over the guard ring anda post-passivation interconnect (PPI) opening on top of the passivationcontact; a first polymer layer over the passivation layer, wherein thefirst polymer layer is over the active area without overlap with theguard ring; a post-passivation interconnect (PPI) guard ring filling thePPI opening within the passivation layer and extending on top of thepassivation layer; and a second polymer layer over the first polymerlayer, the passivation layer, and the PPI guard ring.
 14. Thesemiconductor device of claim 13, wherein the passivation layercomprises a plurality of sub-layers.
 15. The semiconductor device ofclaim 13, wherein the second polymer layer extends to an edge of theguard ring next to a scribe line.
 16. The semiconductor device of claim13, wherein the PPI opening is of a round shape with a diameter about 2um and the PPI guard ring on top of the passivation layer is of arectangle shape with a side of size about 4 um.
 17. The semiconductordevice of claim 13, wherein an edge of the PPI guard ring over thepassivation layer has a distance at least about 2 um to an edge of thefirst polymer layer.
 18. The semiconductor device of claim 13, whereinthe PPI guard ring is made of copper, copper alloys. aluminum, silver,gold, or combinations thereof.
 19. The semiconductor device of claim 13,wherein the first polymer layer is made of an epoxy, polyimide,benzocyclobutene (BCB), polybenzoxazole (PBO), and the like polymer. 20.A method of forming a semiconductor device, comprising: forming apassivation layer on top of a circuit device, wherein the circuit devicecomprises a guard ring and an active area, and the passivation layer isformed over the guard ring and the active area; forming a passivationcontact within the passivation layer connected to the guard ring;forming a first polymer layer over the passivation layer; forming apost-passivation interconnect (PPI) opening within the first polymerlayer over the guard ring; filling the PPI opening with a PPI guardring, wherein the PPI guard ring is connected to the passivation contactand extends on top of the first polymer layer; and forming a secondpolymer layer over the first polymer layer and the PPI guard ring.